1. Field of the Invention
The present invention relates to a variable-displacement inclined plate compressor, and, more specifically, to a variable-displacement inclined plate compressor with an improved structure of cylinder bores of a cylinder block suitable, for use in a refrigerating cycle of an air conditioner for vehicles.
2. Description of Related Art
Variable-displacement inclined plate compressors are known in the art. A known structure of a variable-displacement inclined plate compressor is constructed as depicted in FIG. 4, and such a compressor structure is disclosed, for example, in JP-A-7-91366. In FIG. 4, front housing 2 is connected to the front side of cylinder block 1, and rear housing 3 is connected to the rear side of cylinder block 1 via valve plate 4. A crank chamber 5 is defined by cylinder block 1 and front housing 2. A drive shaft 6, extending in its axial direction X, is disposed in crank chamber 5. Drive shaft 6 is rotatably supported by bearings 7a and 7b. Cylinder bores 8 are defined in cylinder block 1 around a central bore 41, into which one end of drive shaft 6 is inserted. Pistons 9 are slidably inserted into the respective cylinder bores 8.
Rotor 10 is fixed onto drive shaft 6 in crank chamber 5. Rotor 10 rotates synchronously with the rotation of drive shaft 6. Rotor 10 is rotatably supported by bearing 7c relative to front housing 2. Inclined plate 11 is provided around drive shaft 6 at a rear side of rotor 10 in crank chamber 5. Drive shaft 6 is inserted into a through hole 20 defined at the center of inclined plate 11. Supporting portion 20a is formed in through hole 20. Inclined plate 11 is supported on drive shaft 6 via supporting portion 20a, so that inclined plate 11 may be slid along axial direction X of drive shaft 6 and rotated synchronously with the rotation of drive shaft 6. Spring 12 is interposed between rotor 10 and inclined plate 11. Spring 12 urges inclined plate 11 in the direction toward rear housing 3.
Semi-spherical shoe 14 is provided between the radially outer portion of inclined plate 11 and each piston 9. Shoe 14 connects inclined plate 11 and each piston 9 by the slidable engagement of shoe 14 with the side surfaces of inclined plate 11 and the spherical inner surface of each piston 9. Thus, respective pistons 9, slidably engaged with inclined plate 11 via respective shoes 14, may be reciprocally moved in respective cylinder bores 8. Hinge mechanism K is provided on the front side of inclined plate 11. Hinge mechanism K has a pair of brackets 15 positioned at both sides of top dead center position T of inclined plate 11. A first end of guide pin 16 is fixed to each bracket 15, and a second end of guide pin 16 is formed as a spherical portion 16a.
A pair of supporting arms 17 are provided on rotor 10, so that each supporting arm 17 slidably engages corresponding guide pin 16. These supporting arms 17 form the remaining part of hinge mechanism K. Guide hole 17a is defined on the tip portion of each supporting arm 17. Guide hole 17a extends in parallel to a plane defined by axis X of drive shaft 6 and top dead center position T of inclined plate 11, and extends straight in a direction approaching from radially outside of axis X of drive shaft 6. The axial directions of respective guide holes 17a are set, so that top dead center position T of piston 9 does not vary significantly in the front/rear direction despite the inclination of inclined plate 11. Respective spherical portions 16a of respective guide pins 16 are inserted rotatably and slidably into respective guide holes 17a.
When spring 12 is at its maximum extension, rear end recess 11b of inclined plate 11, which is formed at the rear end of through hole 20, comes into contact with C-clip 13 engaged on drive shaft 6. By this contact, inclined plate 11 is restricted from further movement in an inclination angle decreasing direction. When spring 12 is fully contracted, front end surface 11a of inclined plate 11, which is formed at the lower front side surface of inclined plate 11 as an inclined surface, comes into contact with rear end surface 10a of rotor 10. By this contact, inclined plate 11 is restricted from further movement in an inclination angle increasing direction.
The interior of rear housing 3 is divided into suction chamber 30 and discharge chamber 31. Suction port 32 and discharge port 33 are opened on valve plate 4 in correspondence with each cylinder bore 8. A compression chamber, formed between valve plate 4 and piston 9, may communicate with suction chamber 30 and discharge chamber 31 via suction port 32 and discharge port 33. A control valve (not shown) is provided on each suction port 32 to control the opening and closing of suction port 32. A control valve (not shown) is provided also on each discharge port 33 to control the opening and closing of discharge port 33. The opening operation of the control valve for discharge port 33 is restricted by retainer 34. Further, a pressure control valve (not shown) is provided between suction chamber 30 and crank chamber 5 to control the pressure in crank chamber 5.
In such a variable-displacement inclined plate compressor, when inclined plate 11 rotates in accompaniment with the rotation of drive shaft 6, the driving force is transmitted to each piston 9 via each shoe 14, and each piston 9 reciprocally moves in each cylinder bore 8. By the reciprocal motion of each piston 9, gas, for example, refrigerant gas, is sucked from suction chamber 30 into a compression chamber through suction port 32. The gas is compressed in the compression chamber. The compressed gas is discharged into discharge chamber 31 through discharge port 33. During this operation, the volume of the compressed gas discharged into discharge chamber 31 is controlled by the controlling pressure in crank chamber 5 due to the pressure control valve.
When the above-described compressor is assembled, in order to facilitate the insertion of piston 9 and piston rings attached thereon into cylinder bore 8 of cylinder block 1, generally front edge 1b of cylinder bore 8 may be chamfered as a straight-line tapered, chamfered portion. However, in such a straight-line tapered, chamfered portion, the end of the tapered, chamfered portion and a connecting portion of a cylinder liner may be formed as a relatively sharp corner portion. If such a corner portion exists, the sliding resistance of piston 9 against a radial pressing force, generated particularly when piston 9 moves from the bottom dead center position toward the top dead center position, may increase. Such an increase of the sliding resistance of piston 9 may result in the generation of scratches on the surface of the coating of piston 9. Further, an excessive load caused by the sliding resistance of piston 9 may adversely affect the control of the inclination of inclined plate 11, thereby reducing the durability of inclined plate 11.